1. Field of the Invention
The present invention relates to a detector for detecting the relative positions of two different objects, and to an imprint apparatus, and an article manufacturing method.
2. Description of the Related Art
As demands for the micropatterning of semiconductor devices advance, a micropatterning technique of forming a resin pattern on a substrate by molding an uncured resin on the substrate by using a mold is attracting attention, in addition to conventional photolithography techniques. The micropatterning technique is also called an imprint technique, and is capable of forming a microstructure of a few nm order on a substrate. An example of the imprint technique is a photo-curing method. In an imprint apparatus using this photo-curing method, a shot as an imprint region on a substrate is first coated with an uncured ultraviolet-curing resin (an imprint resin or a light curable resin) (the resin is dispensed on the shot). Then, this resin is molded by using a mold. After the resin is cured by ultraviolet irradiation, the mold is released, thereby forming a resin pattern on the substrate.
An imprint apparatus matching this photo-curing method is disclosed in, for example, Japanese Patent Laid-Open No. 2008-522412. This imprint apparatus includes a substrate holding stage, a resin coating mechanism, an imprint head, an ultraviolet radiation unit, and an alignment mark detector. In this imprint apparatus, a substrate and a mold are aligned by using a so-called, die-by die method by which, when pressing the substrate and the mold against each other, marks formed on the substrate and the mold are simultaneously observed for each shot, and a shift between the marks is corrected.
In the imprint apparatus disclosed in Japanese Patent Laid-Open No. 2008-522412, alignment marks are formed on a mold and a substrate. The mark on the mold includes a grating pattern having a grating pitch in a measurement direction. The mark on the substrate includes a checkerboard grating pattern having a grating pitch in each of the measurement direction and a direction (non-measurement direction) perpendicular to the measurement direction. An illumination optical system for illuminating the marks and a detection optical system for detecting diffracted light from the marks are inclined from a direction perpendicular to the mold and the substrate toward the non-measurement direction. That is, the illumination optical system is designed so as to obliquely illuminate the marks in the non-measurement direction. Light obliquely incident on the marks is diffracted in the non-measurement direction by a checkerboard grating pattern formed on the substrate, and the detection optical system detects only diffracted light having a specific order, other than the 0th order in the non-measurement direction.
Also, the grating pitch of the grating pattern formed on the mold and that of the grating pattern formed on the substrate are slightly different in the measurement direction. When these grating patterns having different grating pitches are overlaid, the interference between diffracted light components from the two grating patterns forms an interference fringe (a so-called moire fringe) having a period reflecting the difference between the grating pitches of the grating patterns. Since the phase of this moire fringe changes in accordance with the positional relationship between the grating patterns, the substrate and the mold can be aligned by observing the phase of the moire fringe. A method of detecting relative positions by using the moire fringe as described above has the advantage that alignment can be performed with a high accuracy even when using a detection optical system having a low resolving power.
The detector disclosed in Japanese Patent Laid-Open No. 2008-522412 detects light diffracted in the non-measurement direction by the checkerboard grating pattern formed on the substrate, in a direction not perpendicular to the mold or the substrate. Therefore, a single detector (an illumination optical system and a detection optical system) cannot acquire information on the relative positions of the mold and the substrate in a plurality of directions.